Biological Causes of Depression

Biological Causes of DepressionDepression is often caused by a combination of genetic or biological factors and situational or environmental factors. Research continues to be done that sheds light on the causes of depression. Current understanding is that there are two primary biological causes of depression: changes in the limbic system in the brain and changes in the hormonal system in the body.

The Brain’s Limbic System

The limbic system is the area of the brain that regulates mood, emotions, sex drive and the stress response. This is done primarily through the mechanism of chemical neurotransmitters, which transmit messages in the form of electrical impulses throughout the various specialized neurons in the brain. The neurotransmitters act so fast (within 1/5,000th of a second) that sensations such as pleasure and pain are experienced virtually instantaneously.

There are approximately 30 neurotransmitters that have been identified. Of these, three are associated with clinical depression: norepinephrine, dopamine and serotonin. Neurotransmitters are very difficult to study, and although these three have been liked to depression, the exact cause and effect relationship remains unclear. For instance, some depressed people have lowered levels of norepinephrine while others have elevated levels of norepinephrine.

Much of what is known or hypothesized is based on evidence of the function of anti-depressant medications, which are thought to regulate levels of neurotransmitters. One of the remaining mysteries involves the fact that although anti-depressant medications are very effective for some people, they do not work for everyone, suggesting that neurotransmitter levels produce different effects in different people. If everyone were affected the same way by changing levels of neurotransmitters, then anti-depressants would work for everyone. Furthermore, while anti-depressants alter levels of neurotransmitters almost immediately, most depressed patients do not feel better for several weeks.

It is thought that changes in neurotransmitter levels can cause depression and vise-versa. Many external factors, such as drug use, can cause changes in neurotransmitter levels and lead to depression. This works because most drugs raise levels of neurotransmitters; with repeated use, the brain stops making enough on its own. If the drug is absent, the user will then experience depression due to decreased levels of neurotransmitters. However, drugs are not the only thing that can alter levels of neurotransmitters; for instance, dopamine is released in response to many pleasurable activities, such as sex or eating delicious food. Deteriorating circumstances in a person’s life can cause neurotransmitter levels to plummet.

The Hypothalamus and Hormone Levels

The hypothalamus is a small structure at the base of the brain and is also a part of the limbic system. The hypothalamus controls the release of hormones into the endocrine system of the body. Hormone levels are regulated in a system that has been likened to a thermostat in a house. When hormone levels are adequate, the system shuts down production; when hormone levels fall, production resumes.

Depressed individuals often have abnormal levels of various hormones within their bodies. Furthermore, persons with endocrine disorders sometimes develop depression, and depressed individuals sometimes develop endocrine disorders. Thyroid disorders, Cushing’s syndrome and Addison’s disease all may cause depression.

Treating Depression

Whatever its causes, depression is a serious and potentially dangerous condition that can lead to a greatly reduced quality of life and even suicide. Effective treatment for depression is readily available. If you or someone you know is suffering from depression and needs treatment, please call our toll-free, 24-hour helpline today.